panel overcurrent protection

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1952

Member
Can someone clear my mind on this topic.
I am remodeling a building floor, all electrical
work is being redone. The panel has to be relocated. The old panel was located about five foot from the transformer. The transformer is located above suspended ceilling, (approx. 12ft aff). The panel is going to be located approx. 30 or 35ft away from the transformer. The panel was being feed straight to the panels main breaker.
The same panel is to be used. Question; Do I need
to install a disconnet between the tranformer and
the panel even if the panel has a main breaker?
I would think the overcurrent protecting the transformer, on the primary side, would cover this protection.
I can't find the answer.unless it falls under art. 240.21B4. I find Article 240.21B1,2,3,4 and 5, but not over 25ft indoors, except for high bay. If that's the case, I do not need to provide a disconnet between the transformer and panel as long as I land the secondary feeders on the panel main circuit breader, correct?

[ January 09, 2005, 12:24 AM: Message edited by: 1952 ]
 
H

heco

Member
Re: panel overcurrent protection

240.21 is for Tap Rules of which this Is NOT..
408.16.d Panels supplied through a transformer Will Apply....
Hopes this helps....and Yes you can use the Mains in the Panel..
 
russ

russ

Senior Member
Location
Burbank IL
Re: panel overcurrent protection

240.21(C) would require a disconnect closer to the transformer than your panel is.
 
J

jtester

Senior Member
Location
Las Cruces N.M.
Re: panel overcurrent protection

I agree with russ. This does fall under 240.21(C) you could probably apply either (2) or (6) which gives you either 10' or 25' to the panel, but you must check the requirements closely.
Jim T
 
russ

russ

Senior Member
Location
Burbank IL
Re: panel overcurrent protection

It's to far from the transformer.

Edit to add.

If the inspector red tagged you for not complying with article 240.21(C), what would you say to dispute that.

Edit again to correct article number

[ January 09, 2005, 12:49 PM: Message edited by: russ ]
 
M

mpd

Senior Member
Re: panel overcurrent protection

this would have to comply with 240.21 (C), art.
450 protects the transformer, art. 240 protects
the conductors.
 
1

1952

Member
Re: panel overcurrent protection

Ha guys, thanks for your input. I had forgotten to mention I had looked into
408.16A, which refers to 240.21(C)1.

This is a lighting and appliance panelboard.
I don't know off hand the ocpd rating for the
trans nor the pnl att, I'll have to get back after work monday.
In reference to why I need a disconnect, that
is the reason I am inquiring for help. I am not trying to protect the trans. That is already protected by the primary side. I am trying to
make sure my panel (supplied by the trans), is
properly protected by the nec. It already has
an overcurrent protection (main breaker), but
I want to find out if I need to protect it
because it does not fall within 25ft according
to Art 240.21c6. This is the best possible answer
I can find, but it still not clear since it is
farther then 25ft. I could play it safe and just
put a disconnect between the trans and pnl, but
I thought I could do some help research.
This is what I've looked into so far.
Articles 408.16A/D/ D.exception
240.21C1 240.21C1 thru C6
I believe C6 has part of my answer, but it still over 25ft. I need to check the ocp for the
trans and pnl to compare with 240.21C6.1
I comply with 240.21C6.2 and C6.3
Anyone agrees????
///Arnold///ACT hou.tx

[ January 09, 2005, 07:43 PM: Message edited by: 1952 ]
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Re: panel overcurrent protection

I still don't see why a disconenct is required on the tranformer secondary. OCP is required due to the tap length but not a disconnect.

I can understand why you might put in a fused disconnect since that might be the simplest way to install the OCPD.
 
steve66

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Re: panel overcurrent protection

I think Russ might have meant overcurrent protection when he said disconnect. But I agree with petersonra's post, it is a fuse or breaker that is required. A nonfused disconnect won't help.
 
russ

russ

Senior Member
Location
Burbank IL
Re: panel overcurrent protection

OK that's what I meant, overcurrent protection.

I just said disconnect, because with nothing there now that seemed to be the logical piece to install.
 
D

dillon3c

Senior Member
Re: panel overcurrent protection

Originally posted by 1952:
The transformer is located above suspended ceilling, (approx. 12ft aff).
Click to expand...
--------------------This is why I ask in the other post,no information was offered as to size--(kva)rating..Just caught my eye..
 
1

1952

Member
Re: panel overcurrent protection

New information applies as follows;
transformer size 45kva. protected by a 70a primary breaker, wires from primary side are
awg6, amps requested by trans plate 54a.
3ph 480v primary side.// secondary output 125a
208v awg1 to be used, ocp will be a 125ckt bkr
aprox. 35ft away from trans.
//hou.tx.//
 
1

1952

Member
Re: panel overcurrent protection

New information as requested follows;
The transformer size is 45kva/480 delta/wye.
It is protected by a 70A bkr, 6AWG on the
primary. Nameplate states 54A on Primary,
and 125A output/secondary. On the secondary
side the pnl is protected by a 125A bkr, 1AWG
and is located aprox. 35ft from the trans.
Will this cover everything on the secondary
side as is? I will clear this topic tomorrow.
Thanks for all the imput.
//hou.tx.//
 
J

jtester

Senior Member
Location
Las Cruces N.M.
Re: panel overcurrent protection

1952

I contend the thing that is still a problem is that your secondary conductors go too far before they hit an OCPD. The transformer is protected, but the conductors aren't because they still don't comply with 240.21(C).
Jim T
 
1

1952

Member
Re: panel overcurrent protection

Thank you jtester/Tim, I agree. I think if
I put a dual element fuse on a disconnect after
the transformer will take care of the secondary
wires. I just know this distance should not go
farther then 25ft. Wish it was that easy to tell
them, "You all need to move that new panel within
25ft. to sove this problem." But I'll probably
be without a job the next day, haha. Tks all...
ACT//hou.tx.//
topic closed for me tks...
 
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